White sapote (Casimiroa edulis): performance under various culture salinities and environmental stress conditions in field studies

Abstract

White sapote (Casimiroa edulis) has recently been introduced into the Negev Desert of Israel. Its tolerance to salinity was studied in a short-term sand culture experiment. One-year-old seedlings were irrigated with nutrient solutions of varying NaCl content (electrical conductivity of 1.5 (control), 4, 8 or 12 dS m−1). The increase in shoot length and truck circumference fell to 50% of the control at 4 dS m−1 and to 5–7% of the control at 8–12 dS m−1. Leaves showed damage only at 12 dS m−1. Elevated salinity raised Cl and Na and depressed K concentrations (dry weight basis) in roots and shoots. Concentration of Cl in stems and leaves of salt-stressed plants increased more rapidly than that of Na. Data are also presented on the performance of seedlings planted at three sites in the Negev Desert differing in climate and water quality as follows: Besor — moderate temperatures and good quality water; Ramat-Negev — low winter tempertures (minimum of −7°C) and good quality water; Qetura — high summer temperatures (up to 46°C) and brackish water (4.0 dS m−1). Growth of 3.5-year-old trees in terms of trunk circumference was 1.6 and 1.2-times more vigorous at Besor than at Ramat-Negev and Qetura, respectively. Trees accumulated more Cl in stems and leaves at Qetura than at other sites, although no stress symptoms were observed on leaves. Significant production of floral clusters started in the fourth year and was weakest at Ramat-Negev and most abundant at Qetura.